The present invention relates to a floating caliper disc brake with two brake pistons.
A typical single-piston floating caliper disc brake is described in U.S. Patent No. 4,219,106. The inner side of the floating caliper of this brake, i.e. the side carrying a brake cylinder encompassing the brake piston, is axially guided by two guiding pins detachably fixed to a supporting frame. For supporting the outer side of the floating caliper, the outer brake shoe has two T-shaped projections spaced apart from each other in peripheral direction. The radially inner arms of the projections are guided by axial guide tracks shaped on the supporting frame. The outer side of the brake caliper extends between the radially outer arms of the projections for radial support with a small peripheral clearance between the arms and the caliper to avoid an exertion of tangential forces on the caliper. At the points of support, the caliper must be machined very precisely. Additionally, the width of the caliper is limited to the space between the two radially outwardly extending arms. For a two-piston caliper, it is desirable to make the caliper wider for enhanced stiffness.
A generic two-piston disc brake is known, for instance, from published German patent application No. 39 03 251. The inner side of the floating caliper of this brake is guided as described above. The outer side of the floating caliper is engaged with a so-called spring clip. The spring clip comprises a positioning plate with circular holes that match corresponding nipples shaped on the carrier plate of the outer brake shoe. A pair of nipples on the outer side of the positioning plate is adapted to support the caliper by meshing in the recess openings on the outer side of the brake caliper that allow insertion of a tool for processing the inner surfaces of the brake cylinders. Since the caliper is not supported at its outer edges, it can be designed even wider than the brake shoes. However, the nipples are way smaller than the recess openings which have a partially circular shape, so that slight peripheral shift of the caliper results in a different radial position, for the nipples are arranged decentrally with respect to the circular portions of the recess openings. Additionally, such a spring clip presents an additional part to manufacture and to assemble which results in higher costs.
Therefore, it has been proposed for single-piston floating calipers, for example in U.S. Patent No. 5,111,914, FIG. 7, to provide the brake shoe with a radially outwardly extending protrusion, adapted to mesh in a corresponding cavity in the caliper located in the interior of the brake caliper around the edge of the central recess opening. In this way, the caliper is supported by the brake shoe which itself is supported and guided by guide surfaces shaped on the supporting frame. By this means, the width of the caliper in not limited by the width of the brake shoe either. Unfortunately, this principle cannot be transferred to two-piston floating calipers since they have no central recess opening. If such an arrangement is located only at one of the two recess openings, the support of the brake caliper is too one-sided and the other side has no sufficient radial support. If both recess openings are furnished with such a support arrangement, the system may be overdetermined due to too many positioning means which might have the consequence that supporting frame, caliper and brake shoe do not fit together.